Читать книгу Emergency Medical Services - Группа авторов - Страница 174

Shock is a complex physiological process defined as the widespread reduction in tissue perfusion leading to cellular and organ dysfunction and death. In the early stages of shock, a series of complex compensatory mechanisms act to preserve critical organ perfusion [3]. In general, the following relationships drive this process:

Any condition that lowers cardiac output or peripheral vascular resistance may decrease blood pressure. Alterations of heart rate (very low or very high) can lower cardiac output, and hence can reduce blood pressure secondary to decreased cardiac filling. Decreasing stroke volume may lower cardiac output with a possible reduction in perfusion as well. Cardiac output may be reduced by lower circulating blood volume (e.g., hemorrhage or dehydration), by damage to the heart (e.g., myocardial infarction or myocarditis), or by conditions obstructing blood flow through the thorax (e.g., tension pneumothorax, cardiac tamponade, or extensive pulmonary embolism).

To aid in the evaluation and treatment of shock, it is often useful for the physician and emergency medical services (EMS) personnel to categorize the etiology of the shock condition [4]. Most EMS clinicians are familiar with the “pump‐pipes‐fluid” model of the cardiovascular system, with the pump representing the heart, pipes representing the vascular system, and fluid representing the blood [5]. Categorizing shock into four categories may help to organize assessments and management approaches. Accurate physical assessment is vital for the EMS clinician to determine the categories of the shock state (Table 7.1).